Since the United Nations Conference on Environment and Development (UNCED) in Rio de Janeiro in 1992 and the Kyoto Convention in 1997, the emission of air pollutants has been regulated, and biofuel has received a great deal of attention as a renewable energy source for reducing the emission of carbon dioxide. Currently, there is an urgent need to develop biodiesel that can be used as a clean alternative fuel for diesel vehicles, which account for 30% or more of transportation vehicles in the world and generate 50% or more air pollution. Biodiesel is made from organic materials by esterifying animal and vegetable oils with alcohols such as methanol or ethanol and removing glycerol from the esterified oils, thus obtaining fatty acid methyl esters or fatty acid ethyl esters. Biodiesel has properties similar to petroleum-derived light oil and causes little air pollution upon combustion, and thus when it is mixed with petroleum-based light oil, it can be used as a clean alternative fuel that can significantly reduce vehicle air pollution, which is the main cause of air pollution. Thus, the demand and need for biodiesel is increasing. In addition to an alternative fuel for light oil, biodiesel can be used as raw materials and additives for lubricant oils and can also be used in various applications, including pollution-free solvents and agricultural biochemicals. In addition, biodiesel can also be used as a catalyst to promote bioremediation for cleaning the seashore when contaminated with crude oils. So far, biodiesel has been produced from a variety of animal and vegetable oils by chemical catalytic methods using a strong acid or a strong base. However, in the chemical catalytic methods, a multi-step reaction process that consumes large amounts of energy is required, it is difficult to recover catalysts and byproducts, and a large amount of wastewater is generated, thus causing secondary environmental contamination. Due to these problems, a low-energy-consuming, environmentally friendly new biological process that can satisfy the strong demand for biodiesel is required. In 2006, Rainer et al. reported the production of fatty acid ethyl esters in E. coli (Rainer Kalscheuer et al, Microbiology. 152, 2529-2536, 2006), suggesting that fatty acid ethyl esters can be processed by a biological method. However, the production of alcohols such as ethanol in E. coli is insignificant, and E. coli has low resistance to alcohols. In recent years, studies on the increase in the production of fatty acid ethyl esters in E. coli have been conducted by Eric et al. (Eric J. Steen et al., Nature. 463. 559-556, 2010), but even in an E. coli strain transformed such that ethanol can be produced therein, the production of ethanol was significantly low. This led to a study that reported an increase in the production of fatty acid ethyl esters when ethanol was added to a medium. The present inventors have developed a more efficient system for producing fatty acid ethyl esters as a result of selecting yeast having ethanol resistance and high ethanol productivity as a host for producing fatty acid ethyl esters.
Also, glycerol (C3H8O3), which is used as a substrate in the present invention, is chemically more reduced than glucose (C6H12O6), and thus provides a higher reducing power for the metabolism of microorganisms. Since a lot of materials produced during fermentation are generally required to have reducing power in their metabolism, the use of glycerol as a substrate can lead to a significant improvement in the yield and productivity of desired fermentation products. Currently, as the production of biodiesel increases, the production of glycerol also increases, and thus the price thereof is decreasing rapidly. As described above, because a rapid increase in the production of biodiesel leads to an increase in the production of the byproduct glycerol, the effective treatment of byproducts including glycerol will be issued. Thus, if glycerol can be effectively used to produce useful fermentation products, it can provide a lot of additional effects.